Oxidation catalyst for a compression ignition engine

Abstract

An oxidation catalyst for treating an exhaust gas from a compression ignition engine, which oxidation catalyst comprises: a substrate; a first washcoat region comprising palladium (Pd) and a first support material comprising cerium oxide; and a second washcoat region comprising platinum (Pt) and a second support material.

The invention claimed is: 
     
       1. An oxidation catalyst for treating an exhaust gas from a compression ignition engine, which oxidation catalyst comprises:
 a flow-through substrate monolith having an inlet end and an outlet end; 
 a first washcoat region free of platinum comprising palladium (Pd) and a first support material comprising cerium oxide; and 
 a second washcoat region comprising platinum (Pt) and a second support material, 
 wherein the second washcoat region is arranged to contact inlet exhaust gas before the first washcoat region, wherein: 
 the second washcoat region is a second washcoat zone disposed or supported at the inlet end of the flow-through substrate monolith and the first washcoat region is disposed or supported downstream from the second washcoat zone. 
 
     
     
       2. The oxidation catalyst according to  claim 1 , wherein the second washcoat region further comprises palladium (Pd). 
     
     
       3. The oxidation catalyst according to  claim 2 , wherein the mass of platinum (Pt) is greater than the mass of palladium (Pd) in the second washcoat region. 
     
     
       4. The oxidation catalyst according to  claim 2 , wherein the ratio by mass of platinum to palladium in the second washcoat region is 20:1 to 1.1:1. 
     
     
       5. The oxidation catalyst of  claim 1 , wherein the second support material comprises a refractory metal oxide. 
     
     
       6. The oxidation catalyst according to  claim 5 , wherein the refractory metal oxide is selected from the group consisting of alumina, silica, titania, zirconia, ceria and mixed or composite oxides of two or more thereof. 
     
     
       7. The oxidation catalyst according to  claim 6 , wherein the refractory metal oxide is alumina. 
     
     
       8. The oxidation catalyst of  claim 1 , wherein the first washcoat region comprises an amount of palladium (Pd) of 0.25 to 1.9% by weight. 
     
     
       9. The oxidation catalyst according to  claim 1 , wherein the first washcoat region comprises an amount of palladium (Pd) of 0.2% to 15% by weight. 
     
     
       10. The oxidation catalyst according to  claim 9 , wherein the first washcoat region comprises palladium (Pd) in an amount of 5 to 300 g ft −3 . 
     
     
       11. The oxidation catalyst according to  claim 10 , wherein the second washcoat region comprises platinum (Pt) in an amount of 5 to 300 g ft −3 . 
     
     
       12. The oxidation catalyst according to  claim 1 , wherein a total amount of first support material and second support material is 0.2 to 8 g in −3 . 
     
     
       13. An exhaust system comprising an oxidation catalyst of  claim 1 , and an emissions control device disposed downstream from the outlet of the oxidation catalyst, wherein the emissions control device is a selective catalytic reduction (SCR) catalyst, a selective catalytic reduction filter (SCRF™) catalyst, a diesel particulate filter (DPF), or a catalysed soot filter (CSF). 
     
     
       14. A vehicle comprising a compression ignition engine and either:
 (a) an oxidation catalyst of  claim 1 ; or 
 (b) an exhaust system according to  claim 13 . 
 
     
     
       15. A method of modulating the content of NO x  in an exhaust gas from a compression ignition engine for an emissions control device, which method comprises:
 (a) controlling the NO x  content of an exhaust gas by contacting the exhaust gas with an oxidation catalyst according to  claim 1  to produce a treated exhaust gas; and 
 (b) passing the treated exhaust gas to an emissions control device, which is a selective catalytic reduction (SCR) catalyst, a selective catalytic reduction filter (SCRF™) catalyst, a diesel particulate filter (DPF), or a catalysed soot filter (CSF).